It is known that non-asbestos papers and/or sheets may be produced from water-swellable inorganic materials and, in particular, swelled silicate gels. For example, U.S. Pat. No. 4,239,519 is directed to the preparation of synthetically derived, inorganic, crystal-containing gellable, water-swelling sheet silicates and certain articles, such as papers, fibers, films, boards, and laminates, produced therefrom. These non-asbestos papers and/or sheets exhibit good high temperature stability and good chemical resistance. Furthermore, since asbestos fibers are not utilized in their manufacture, such articles will not have the health hazards which are associated with asbestos containing articles.
U.S. Pat. No. 4,239,519 teaches the method for making the precursor gellable silicates used to produce said papers or sheet articles, as involving three fundamental steps: (a) a fully or predominantly crystalline body is formed which contains crystals consisting essentially of a lithium and/or sodium water-swelling mica selected from the group of fluorhectorite, hydroxyl hectorite, boron fluorphlogopite, hydroxyl boron phlogopite, and solid solutions between those and other structurally compatible species selected from the group of talc, fluortalc, polylithionite, fluorpolylithionite, phlogopite, and fluorphlogopite; (b) that body is contacted with a polar liquid, normally water, to cause swelling and disintegration of the body accompanied with the formation of a gel; and (c) the solid: liquid ratio of the gel is adjusted to a desired value depending upon the application therefore. Glass-ceramics are the preferred crystalline starting bodies. Those products are then contacted with a source of large cations, i.e., with an ionic radius larger than that of the lithium cation, to cause macro flocculation of the gel and an ion exchange reaction to take place between the large cations and the Li.sup.+ and/or Na.sup.+ ions from the interlayer of the crystals.
Alternatively, U.S. Pat. Nos. 3,325,340 and 3,454,917 teach producing aqueous dispersions of vermiculite flaked crystals which have been caused to swell due to the introduction therein of interstitial ions such as: (1) alkylammonium cations having between 3 and 6 carbon atoms inclusive in each carbon group such as methylbutylammonium, n-butylammonium, propylammonium and iso-amylammonium; (2) the cationic form of amino-acids, such as lysine and ornithine; and/or (3) lithium.
While the articles, such as papers, sheets and films, prepared via the prior art processes set forth above exhibit excellent heat resistance and are useful in a wide variety of applications, it has been discovered that such articles generally do not exhibit good sealing characteristics, thus curtailing their use as gasket materials. The prior art articles also exhibit a certain amount of water sensitivity which is generally exhibited by the articles having a considerable loss of strength and general deterioration of mechanical and electrical properties when exposed to high humidity environments or submerged in water or other polar liquids. This sensitivity to water correspondingly limits the utility of these articles in certain applications, such as, for example, head gaskets, electrical insulators, environmental protective coatings, and washable and environmentally stable building materials.